1 18-Gtrbr-05 Motorcycle Brake Systems
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18-GTRBR-05 MOTORCYCLE BRAKE SYSTEMS gtr - TECHNICAL REPORT - 1. Introduction During the 58th session of the Working Party on Brakes and Running Gear (GRRF), a formal proposal for a global technical regulation (gtr) concerning Motorcycle Brake Systems was presented, along with the accompanying “Statement of Technical Rationale and Justification”. This Technical Report serves to provide additional detail regarding the technical rationale for the respective requirements within the proposed gtr. 2. General The proposed gtr on Motorcycle Brake Systems consists of a compilation of the most stringent and relevant tests procedures and performance requirements from current standards and regulations. The informal group reviewed the existing requirements on various levels, including estimating the relative severity of the requirements as well as considering the original rationales and appropriateness of the tests to modern conditions and technologies. As a result of the comparison process, the selected performance requirements within the gtr are mainly developed from the UN/ECE Regulation No. 78 (ECE), the United States Federal Motor Vehicle Safety Standard FMVSS 122 (FMVSS) and the Japanese Safety Standard JSS 12-61 (JSS). The selected format for the gtr text is based on the Alternative format for regulations with many different requirements and test procedures, as described in TRANS/WP.29/883, and was chosen to facilitate quick reference and understanding of the requirements. While developing the gtr, the informal group endeavoured to clarify discrepancies in the referenced tests, to assure a better understanding and the consistency in the way the respective tests are conducted. The gtr is comprised of several fundamental tests, each with their respective performance requirements. These tests are listed below, along with the national regulation on which they are based: 1. dry stop test with each brake control operated separately (ECE R78 / JSS 12-61) 2. dry stop test with all brake controls activated simultaneously (FMVSS 122) 3. high speed test (JSS 12-61) 4. wet brake test (ECE R78 / JSS 12-61) 5. heat fade test (ECE R78 / JSS 12-61) 6. parking brake test (ECE R78 / JSS 12-61) 7. ABS tests (ECE R78 / JSS 12-61) 8. partial failure test – split service brake systems (FMVSS 122) 9. servo failure test (New) 1 2.1 gtr Test Parameters To maintain the integrity of the referenced test, the parameters selected for each performance test are almost entirely as specified in the respective national regulation on which the test was based. Although the national regulations share many similarities, there are several differences in the terminology and their definitions. The informal group sought to streamline the gtr with the use of common terminology and definitions. Whenever possible, these were obtained from the document Special Resolution No. 1 (S.R.1) concerning the common definitions of vehicle categories, masses and dimensions. Alternately, terminology and definitions were adopted from recognized sources such as the International Organization for Standardization (ISO), the Society of Automotive Engineers (SAE) and others. Terminology borrowed from S.R.1 includes “mass in running order” and “gross vehicle mass”. Mass in running order is defined as the sum of the unladen vehicle mass and the driver’s mass, which are further defined in S.R.1. Gross vehicle mass is the maximum mass of the fully laden vehicle as declared by the manufacturer. Definitions for existing terminology were revised or updated where necessary, such as for antilock brake system (ABS), vehicle maximum speed (Vmax) and peak friction coefficient (PFC). New terminology was also introduced when required. One such example deals with defining the motorcycle test mass: In this case, the terminology “lightly-loaded vehicle” (FMVSS 122), “unladen vehicle” (ECE R78) and “unloaded” (JSS 12-61) essentially share the same meaning, which is the sum of the “mass in running order” and all of the test equipment, including outriggers, if so equipped. In an effort to streamline the gtr, the Contracting Parties agreed to the term “lightly-loaded vehicle mass”, as this does not conflict with existing definitions in S.R.1, nor other recognized sources. 2.2 Measurement of Deceleration and Stopping Distance The ECE and JSS test methods allow brake performance to be measured through the use of either deceleration or stopping distance, whereas the FMVSS evaluates performance through stopping distance only. The ECE and JSS measure deceleration slightly differently. The ECE utilizes the mean fully developed deceleration (MFDD), which is the vehicle deceleration calculated between 10 and 80 percent of the vehicle initial speed. The JSS uses the vehicle mean saturated deceleration (MSD), which can be obtained several ways depending on the instrumentation employed. Both methods measure a steady state deceleration rate, by excluding the transient period during the initial stage of the brake application and the very end of the braking maneuver. Nevertheless, the different methods can provide slightly different results. In order to maintain consistency in the results, the MFDD was adopted to measure braking deceleration performance, where required. The FMVSS stopping distance is based on an average deceleration rate for the entire stopping maneuver, from the moment a force is applied to the brake control to the moment the vehicle comes to a complete stop. The ECE and JSS stopping distance are based on the MFDD (or MSD) and also account for a system reaction time. 2 To maintain the integrity of the referenced test, the performance requirements are almost entirely as specified in the respective national regulation on which the test was based. 2.3 Corrected Measured Distance Deceleration or stopping distance performance requirements are related to a specific initial test speed. While professional test riders can approach this initial test speed, it is unlikely that the test will be started at the exact speed specified. A braking distance correction factor is specified in JSS 12-61 to compensate for the difference between the specified test speed and the actual speed where the brakes were applied. Although not specified in the regulations, the USA and Canada utilise the correction factor specified in SAE J299 – Stopping Distance Test Procedure. Each method was evaluated, including the distance correction factor for motorcycle brake testing found in ISO 8710:1995, Motorcycles – Brakes and braking devices - tests and measurement methods. The SAE offers the most basic method for estimating the corrected distance, and as a result the method is applicable to a speed tolerance of ± 3.2 km/h (± 2 mph). The ISO and JSS methods are based on the same principles, but also take into consideration the system reaction time. These methods are applicable to a wider speed tolerance of ± 5 km/h. However, a small error in handling the system reaction time is apparent in the ISO equation, which results in higher than expected corrected values. Based on this analysis, the informal group agreed that the correction factor equation within JSS 12-61 was the most appropriate for the gtr. 2.4 Test Surface – Peak Friction Coefficient Peak Friction Coefficient (PFC) is a measure of the coefficient of friction of the test surface and is an important parameter for assessing brake performance of a vehicle. FMVSS 122 currently requires that the road tests be conducted on an 8-foot-wide level roadway with a skid number of 81. The road test surface conditions specified do not apply to the burnish procedure. For parking brake tests, the test surface is clean, dry, smooth Portland concrete cement. ECE R78 and JSS 12-61 do not specify the coefficient of friction for the test surface but describe the test surface as level, dry, and affording good adhesion. Test lane width is also specified as 2.5 m (8 feet). ECE R78 and JSS 12-61 rely on a subjective description of the test surface coefficient of friction. Under the self-certification system currently used by Contracting Parties such as the United States and Canada, the test surface is defined, objectively, to reduce variability of the results when testing motorcycle brake systems for compliance to their national standard. Given that the test surface coefficient of friction affects the attainable braking performance limit of a vehicle, specifying a value in the gtr will prevent unreasonable variability in the test results, which may be due to test surface variability and not due to the motorcycle’s actual braking ability. The Contracting Parties agreed to define the test surface using PFC instead of skid number as currently specified in FMVSS 122. The PFC is a measure of tire-to-road surface friction based on the maximum deceleration of a rolling tire whereas skid number is a measure of 3 the tire-to-road surface friction based on a skidding tire. Therefore, PFC is a more relevant surface friction measurement for non-locked-wheel tests, as those included in this gtr. The Contracting Parties agreed that specifying a test surface with a nominal PFC 0.9 is an appropriate and objective value for the dry test surface for the motorcycle braking tests. The United States Federal motor vehicle safety standards that currently use PFC specify that the road test surface must have a PFC of 0.9 when measured using American Society for Testing and Materials (ASTM) E1136 standard reference test tire, in accordance with ASTM Method E1337-90, at a speed of 40 mph without water delivery. However, since the ASTM test method is not widely used outside of North America and there is no common test method used in Europe or Japan, the Contracting Parties agreed to specify the PFC for the test surface but to leave it to the national regulation to determine the test method that should be used to measure the PFC. 2.5 Test Sequence There is no specified test order in the ECE R78.